Radiation heat transfer coefficient, object to duct

Radiation heat transfer coefficient from cable surface to inner wall of the duct used for riser/J-tube.

Symbol
$h_{rad_{od}}$
Unit
W/(K.m$^2$)
Formulae
$4 K_{r} \sigma \left(\frac{\theta_{di}}{2} + \frac{\theta_{e}}{2} + 273\right)^{3}$
$\sigma$